Ahhh, yes a 21 slide will fit a 20 frame just fine. I see 21 complete slides on GunBroker fairly often, so you don't need a Timerwolf frame.
You could suppress a 10mm, but as always a suppressor is most effective with subsonic ammunition, so if you handload you could do that.
Sights are always a personal preference, but you can't go wrong with anything from Ameriglo.
The G40 Longslide isn't shipping yet, I heard June but that may be wrong.
"Condemnation without investigation is the height of ignorance."